Optical data transceiver modules convert optical signals received via an optical fiber into electrical signals and convert electrical signals into optical signals for transmission via an optical fiber. In the transmitter portion of a transceiver module, a light source such as a laser performs the electrical-to-optical signal conversion. In the receiver portion of the transceiver module, a light receiver such as a photodiode performs the optical-to-electrical signal conversion. A transceiver module commonly also includes optical elements, such as lenses, as well as electrical circuitry such as drivers and receivers. A transceiver module also includes one or more fiber ports to which an optical fiber cable is connected. The light source, light receiver, optical elements and electrical circuitry are mounted within a module housing. The one or more fiber ports are located on the module housing.
As illustrated in FIG. 1, transceiver modules are known in which the receiver 10 performs a demultiplexing function. Optical signals 12 comprising four different modulated wavelengths λ1, λ2, λ3 and λ4 are received and reflected by a reflective surface 14 onto a reflector or mirror 16. (The terms “reflective surface,” “reflector” and “mirror” are used synonymously herein, as any of these elements can comprise any of various types of structures that reflect optical signals 12.) Mirror 16 first reflects optical signals 12 onto a first filter 18, which is transparent to the single wavelength λ1 and reflective to the other wavelengths λ2, λ3 and λ4. Thus, the portion of optical signals 12 that impinge on first filter 18 and consist of wavelength λ1 pass through first filter 18 and impinge on a first light receiver or opto-electronic detector 20. The remaining portion of optical signals 12 that impinge on first filter 18 and consist of wavelengths other than λ1 are reflected by first filter 18 and impinge on mirror 16. Mirror 16 reflects that remaining portion of optical signals 12 onto a second filter 22, which is transparent to the single wavelength λ2 and reflective to at least λ3 and λ4. Thus, the portion of optical signals 12 that impinge on second filter 22 and consist of wavelength λ2 pass through second filter 22 and impinge on a second light receiver or opto-electronic detector 24. The remaining portion of optical signals 12 that impinge on second filter 22 and consist of wavelengths other than λ2 are reflected by second filter 22 and impinge on mirror 16. Mirror 16 reflects that remaining portion of optical signals 12 onto a third filter 26, which is transparent to the single wavelength λ3 and reflective to at least λ4. Thus, the portion of optical signals 12 that impinge on third filter 26 and consist of wavelength λ3 pass through third filter 26 and impinge on a third light receiver or opto-electronic detector 28. The remaining portion of optical signals 12 that impinge on third filter 26 and consist of wavelengths other than λ3 are reflected by third filter 26 and impinge on mirror 16. Mirror 16 reflects that remaining portion of optical signals 12 onto a fourth filter 30, which is transparent to the single wavelength λ4. Thus, the portion of optical signals 12 that impinge on fourth filter 30 and consist of wavelength λ4 pass through fourth filter 30 and impinge on a fourth light receiver or opto-electronic detector 32. Although in receiver 10 shown in FIG. 1 four wavelengths are demultiplexed, other receivers are known in which a number of wavelengths other than four are demultiplexed in a similar manner.
To achieve proper operation, it is important that the surfaces of filters 18, 22, 26 and 30 be very precisely parallel to the surface of mirror 16. Achieving a precisely parallel orientation can present manufacturing challenges. It would be desirable to provide an optical demultiplexing device that promotes achieving such an orientation consistently and quickly in manufacturing.